U.S. patent application Ser. No. 12/916,984 (which has been incorporated herein by reference) has been published as United States Patent Application Publication No. 2011/0100874. The reader is presumed to be familiar with the disclosure of this published application. This published application will be referred to herein as the “874 application.”
The demand for energy (and the hydrocarbons from which that energy is derived) is continually rising. However, hydrocarbon raw materials used to provide this energy often contain difficult-to-remove sulfur and metals. For example, sulfur can cause air pollution and can poison catalysts designed to remove hydrocarbons and nitrogen oxide from motor vehicle exhaust, necessitating the need for expensive processes used to remove the sulfur from the hydrocarbon raw materials before it is allowed to be used as a fuel. Further, metals (such as heavy metals) are often found in the hydrocarbon raw materials. These heavy metals can poison catalysts that are typically utilized to remove the sulfur from hydrocarbons. To remove these metals, further processing of the hydrocarbons is required, thereby further increasing expenses.
Currently, there is an on-going search for new energy sources in order to reduce the United States' dependence on foreign oil. It has been hypothesized that extensive reserves of shale oil, which constitutes oil retorted from oil shale minerals, will play an increasingly significant role in meeting this country's future energy needs. In the U.S., over 1 trillion barrels of usable, reserve shale oil are found in a relatively small area known as the Green River Formation located in Colorado, Utah, and Wyoming. As the price of crude oil rises, these shale oil resources become more attractive as an alternative energy source. In order to utilize this resource, specific technical issues must be solved in order to allow such shale oil reserves to be used, in a cost effective manner, as hydrocarbon fuel. One issue associated with these materials is that they contain a relatively high level of nitrogen, sulfur and metals, which must be removed in order to allow this shale oil to function properly as a hydrocarbon fuel.
Other examples of potential hydrocarbon fuels that likewise require a removal of sulfur, nitrogen, or heavy metals are bitumen (which exists in ample quantities in Alberta, Canada) and heavy oils (such as are found in Venezuela).
The high level of nitrogen, sulfur, and heavy metals in shale oil, bitumen and heavy oil (which may collectively or individually be referred to as “oil feedstock”) makes processing these materials difficult. Typically, these oil feedstock materials are refined to remove the sulfur, nitrogen and heavy metals through a process known as “hydro-treating.”
Hydro-treating may be performed by treating the material with hydrogen gas at an elevated temperature and an elevated pressure using catalysts such as Co—Mo/Al2O3 or Ni—Mo/Al2O3.
In the present invention, the oil feedstock is mixed with an alkali metal (such as sodium) and hydrogen gas. This mixture is reacted under modest pressure (and usually at an elevated temperature). The sulfur and nitrogen atoms are chemically bonded to carbon atoms in the oil feedstocks. The sulfur and nitrogen heteroatoms are reduced by the alkali metals to form ionic salts (such as Na2S, Na3N, Li2S, etc.). To prevent coking (e.g., a formation of a coal-like product), the reaction occurs in the presence of hydrogen gas that can form bonds with the carbon atoms of the oil feedstock previously bonded to the heteroatoms. The hydrogen atom bonds to the carbon atoms that were previously bonded to the heteroatoms, thereby increasing the hydrogen-to-carbon ratio of the oil feedstock and decreasing the heteroatom to carbon ratio of the resulting organic feedstock. After the hydro-treating reaction, the organic phase (oil feedstock) is less viscous and may be sent for further refining into a hydrocarbon fuel material.
The ionic salts formed in the hydro-treating process may be removed from the organic products by filtering, or first mixing the treated feedstock with hydrogen sulfide to form an alkali hydrosulfide, which forms a separate phase from the organic phase (oil feedstock). This reaction is shown below with sodium (Na) being the alkali metal, although other alkali metals may also be used:Na2S+H2S→2NaHS (which is a liquid at 375° C.)Na3N+3H2S→3NaHS+NH3 The nitrogen product is removed in the form of ammonia gas (NH3) which may be vented and recovered, whereas the sulfur product is removed in the form of an alkali hydro sulfide, NaHS, which is separated for further processing. Any heavy metals will also be separated out from the organic hydrocarbons by gravimetric separation techniques.
As part of the process, alkali metals are used. An advantage of using alkali metals such as sodium or lithium instead of hydrogen to reduce the heteroatoms is alkali metals offer a greater reduction strength. In other words, the alkali metals are better able to reduce the heteroatoms and form alkali metal nitrides or alkali metal sulfides. Further, by using alkali metals, there is less need to saturate rings with hydrogen to destabilize them so that the heteroatoms can be reduced, making it possible to remove heteroatoms with significantly less hydrogen.
It should be noted that the alkali metal treatment process is known in the industry and is described, for example, in U.S. Pat. No. 3,787,315, U.S. Patent Application Publication No. 2009/0134040 and U.S. Patent Application Publication No. 2005/0161340. (These documents are expressly incorporated herein by reference.)
A disadvantage of using the hydro-treating process is that hydrogen gas is a necessary reactant needed for the hydro-treating process. However, hydrogen gas can be expensive. Typically, hydrogen gas is formed by reacting hydrocarbon molecules with water. For example, in the United States, 95% of the hydrogen is formed using the Steam-Methane Reforming Process from natural gas. In the first step known as the reforming step, methane (CH4) in natural gas is reacted with steam (H2O) at 750° C.-800° C. to produce synthesis gas (syngas). Syngas is a mixture primarily comprised of hydrogen gas (H2) and carbon monoxide (CO). In the next step, known as the water gas shift reaction, the carbon monoxide produced in the first reaction is reacted with steam (H2O) over a catalyst to form hydrogen gas (H2) and carbon dioxide (CO2). This second process (e.g., the water gas shift reaction) occurs in two stages: the first stage occurring around 350° C. and the second stage occurring at about 200° C.
The overall reaction for the Steam-Methane Reforming Process is as follows:CH4+2H2O→4H2+CO2 Thus for every (theoretical) mole of hydrogen gas produced, 0.25 moles methane and 0.5 moles of water are required. Also, for every mole of hydrogen gas produced, 0.25 moles of carbon dioxide are produced and released to the atmosphere. It should be noted that the Steam-Methane Reforming Process is typically only 65-75% efficient. Thus at 70% efficiency, the Steam-Methane Reforming Process will actually utilizes 0.36 moles of methane and 0.71 moles of water while releasing 0.36 moles of carbon dioxide for every mole of hydrogen produced.
This production of carbon dioxide during the hydro-treating process is considered problematic by many environmentalists due to rising concern over carbon dioxide emissions and the impact such emissions may have on the environment.
An additional problem in many regions is the scarcity of water resources. For example, in the region of Western Colorado and Eastern Utah where parts of the Green River Formation of shale oil is located, the climate is arid and the use of water in forming hydrogen gas can be expensive.
Alternatively, some industrialists have used an electrolysis process to provide the hydrogen gas supply needed for their hydro-treating process. This electrolysis reaction involves the electrolytic decomposition of water. In this electrolytic reaction, water is split to form hydrogen at a cathode and oxygen at an anode:H2O→H2+1/2)2 
In this reaction, electrical energy is used to split the water. If the cell runs at 90% efficiency and runs at about 1.4 Volts, then the electrical energy required is about 72 kcal per mole of created hydrogen. For every mole of hydrogen produced in this electrolysis reaction, one mole of water is consumed. Because one mole of water is consumed to produce hydrogen in this method, more water is required to produce the hydrogen gas via electrolysis than is required to produce the hydrogen using the Steam-Methane Reforming Process (which requires 0.71 moles water). Thus, in arid climates where the cost of water is high, using an electrolysis process to produce hydrogen may not be economically feasible.
While conventional hydro-treating processes are known, they are expensive and require large capital investments in order to obtain a functioning hydro-treating plant. There is a need in the industry for a new process that may be used to remove heteroatoms such as sulfur and nitrogen from oil feedstocks, but that is less expensive than hydro-treating. Such a process is disclosed herein.
Additionally, naphthenic acids must be removed from many organic streams that are produced by refineries. Naphthenic acids (“NAPs”) are carboxylic acids present in petroleum crude or various refinery streams. These acids are responsible for corrosion in refineries. A common measure of acidity of petroleum is called the Total Acid Number (“TAN”) value and is defined as the milligrams (mg) of potassium hydroxide needed to neutralize the acid in one gram of the petroleum material. (Other acids found in the oil feedstock may also contribute to the TAN value). All petroleum streams with TAN >1 are called high TAN. NAPs are a mixture of many different compounds and cannot be separated via distillation. Moreover high TAN crudes are discounted over Brent Crude prices. For example, Doba crude with a TAN of 4.7 is discounted by $19 per barrel on a base price of $80 for Brent crude.
NAPs boil in the same range as that of kerosene/jet fuel. (However, kerosene/jet fuels have very stringent TAN specifications.) Attempting to neutralize these acids using aqueous caustic or other bases form salts. These salts in presence of water, lead to formation of stable emulsions. Additional methodologies of NAP reduction include hydrotreating or decarboxylation that are both destructive methodologies and the NAPs cannot be recovered using these methods. Solvent extraction or adsorption methodologies lead to high costs and energy usage for sorbent regeneration or solvent boiling. A new method for NAPs removal with lower energy consumption wherein NAPs can be recovered and processed as commercial products is required. Accordingly, a new method of neutralizing and/or removing NAPs is needed. Such a method and device is disclosed herein.